1. Field of the Invention
This invention is an improved brake shoe that greatly simplifies brake shoe replacement.
2. Discussion of the Prior Art
Drum brakes and disc brakes are well known in the automotive field. Drum brakes usually include a pair of brake shoes, each of which has an outer brake lining of friction brake material. The shoes are supported by a back plate that is stationary relative to the vehicle chassis, and the shoes are positioned inside a drum that rotates with the wheel and is concentric with the wheel hub. When the brake is applied, the shoes and consequently the brake linings are pressed against the inside surface of the drum to generate a frictional braking force on the wheel of the vehicle.
Disc brakes usually include a caliper that supports a pair of brake pads, each of which has an inner brake lining of friction brake material. The caliper is supported such that it is essentially stationary relative to the vehicle chassis; some limited movement of the caliper parallel to the axis of rotation of the disc is allowed in floating caliper installations to ensure that the disc is gripped evenly on both sides. The brake pads are positioned on either side of the brake disc, which is fixed to and rotates with the wheel and which is concentric with the wheel hub. When the brake is applied, the pads forcefully grip the disc on both sides such that the pads are pressed against respective sides of the disc to generate a frictional braking force on the wheel of the vehicle.
In the typical disc brake the disc is part of a brake rotor that has a central portion that has holes through which the wheel studs extend and that is used to attach the rotor to the wheel once the lug nuts of the wheel are tightened down on the studs. The central portion is in the form of a hollow cylinder extending outward from the annular disc that is capped by a plate having holes for the studs at the end of the hollow cylinder distal from the annular disc. In recent years, several automakers have used the central portion of the disc brake rotor as a drum for a secondary drum brake used in combination with the disc brake on the same wheel. The secondary drum brake is provided with a manual actuation system that is separate from the hydraulic actuation system of the disc brake and is intended to act as a parking brake or an emergency brake. Some manufacturers use a secondary drum brake that uses two brake shoes that are identical in design and operation to typical prior art drum brakes.
U.S. Pat. No. 5,246,093, issued on Sep. 21, 1993, to Nui Wang, illustrates a secondary drum brake that uses a one-piece brake shoe. The brake shoe of Wang has a body that is in the form of a split ring that has a C-shaped form in plan view. Brake linings of friction brake material, also referred to as brake lining material, are mounted on the outer surface of the brake shoe body. When the brake is applied, the actuator pushes the ends of the brake shoe body apart; thus, the actuator presses the brake linings against the inner surface of the central portion of the disc brake rotor, also referred to as the hub of the brake rotor, to generate a frictional braking force on the wheel of the vehicle.
In the brake shoe of Wang, which is now in use in some models of vehicles on the market today, the gap between the ends of the brake shoe, also referred to as the ends of the brake shoe body, is smaller than the diameter of the axle driving the wheel, and the diameter of the center opening of the brake shoe, also referred to as the inner diameter of the brake shoe, is smaller than the outside diameter of the wheel hub. Accordingly, to properly replace the one-piece brake shoe of the type shown by Wang the wheel hub and the axle must first be removed; then, the worn-out brake shoe can be replaced by a new brake shoe, followed by reinstalling the axle and the wheel hub. This procedure undesirably increases the cost of brake shoe replacement because it requires an excessive amount of labor compared with conventional brake shoes.
Some automobile repair shops use an alternative replacement procedure in order to save on labor costs. This procedure involves forcing apart the ends of the brake shoe in order to the get the replacement shoe around the axle; thus, this procedure obviates the need for removing the wheel hub and the axle. However, this procedure causes the brake shoe to be warped such that the brake shoe may interfere with the brake drum or rotor hub even when the brake is not being applied in view of the fact that the clearance between the brake lining and the hub is on the order of several hundredths of an inch when the brake is not being applied. This alternative procedure also causes problems with adjustment of the brake after shoe replacement because the warped condition of the brake shoe makes it harder to find an adjustment setting for the brake actuator that keeps the break lining out of engagement with the rotor hub when the brake is not being applied and that presses the brake lining against the inner surface of the rotor hub with the required force within the range of motion of the actuator or the actuator lever. In addition, once the one piece brake shoe of Wang is warped, the original shape of the brake shoe will be nearly impossible to recover. The ends of the brake shoe body must be forced apart or forced toward one another until a satisfactory shape approaching the original shape of the shoe is obtained by trial and error. Needless to say, all these adjustments are difficult, laborious, and time-consuming, so that the advantages of warping the brake shoe in the first place are negated.
Furthermore, the brake linings of the brake shoe of Wang are ground to a circular arc matching the inner surface of the brake rotor hub or drum while the brake shoe is held in a jig that holds the brake shoe body in the same geometric configuration as the brake shoe body assumes when the brake is applied. This grinding procedure ensures that the surface of the brake linings evenly contacts the inner surface of the brake rotor hub or drum when the brake is applied, so that both the brake linings and the inner surface of the brake rotor hub or drum wear evenly and last longer. The benefits of this painstaking grinding step are negated when the brake shoe is warped in order to the get the brake shoe around the axle because most likely the original shape of the brake shoe and brake linings cannot be recovered with the exactness required.